More particularly, the absorbent covering of the invention is preferably for mounting on board a rotorcraft. On being installed in particular on the walls of the cabin, the absorbent covering attenuates the dynamic deformation thereof so as to increase wall lifetime and reduce noise inside the cabin.
Naturally, the invention is not limited to this particular application, and it can be used for any other application whenever it is desired to reduce the dynamic deformation of a body. By its design, it is possible to consider using the absorbent covering on the walls of a washing machine, for example, since that type of electrical household appliance is subjected to high levels of vibration.
A first known system is constituted by a one-piece elastomer plate arranged on the structure. The damping power of the elastomer diminishes the dynamic deformation of the structure, regardless of the manner in which the structure is stressed mechanically, in particular by dissipating energy in the form of heat.
Nevertheless, the effectiveness of that first system is limited since the oscillation of the structure leads to small movements only in the elastomer. Thus, energy dissipation in the elastomer plate is low.
To improve that first system, it is common practice to use a second system. The second system comprises a visco-constraint elastomer, i.e. an elastomer plate having its top portion previously bonded onto a metal support. The bottom portion of the elastomer plate, opposite from the top portion, is then secured on a structure.
During dynamic deformation, e.g. bending of the structure generated by vibration, the top face is held by the metal support. This condition providing additional limits induces a state of internal stresses within the elastomer that is greater than in the preceding circumstances. Consequently, the amount of vibrational energy that is dissipated in the elastomer plate is increased.
The second system does indeed present better efficiency than the first system. Nevertheless, for applications that require large amounts of vibrational energy to be dissipated, it is still found to be insufficient.
Document FR 2 870 308 discloses a third damper system.
The absorbent covering secured on a structure is provided with an absorbent layer of elastic material that includes a dissipater mesh pattern. That mesh pattern, arranged in the elastic material, is constituted by a plurality of nodes and of dissipater elements.
The amount of energy dissipated in the absorbent layer is large since the elastic material of the absorbent layer is deformed firstly by a lever arm effect caused by the nodes that hold the dissipater elements away from the structure, and secondly by the dissipater elements that take the stresses transmitted by the nodes and spread them throughout the elastic material, while also amplifying the stresses by a geometrical effect.
That system is very effective, but the absorbent layer represents a mass that is not negligible and that can be troublesome in particular applications.